In the field of RFID (an abbreviation of Radio Frequency Identification) devices, radiofrequency transponders are conventionally used for the identification, monitoring and control of objects. These devices permit faster and more reliable automatic control.
Such a radiofrequency transponder usually consists of at least one electronic chip and an antenna, in the form of a magnetic loop or a radiating antenna, fastened to the object to be identified.
The communication performance of the radiofrequency transponder is expressed as a maximum distance of communication of the radiofrequency transponder with a radiofrequency reader for a given signal communicated to or by the radiofrequency reader.
In the case of highly extensible products such as tires, there is a need to identify the product throughout its life, from manufacture to withdrawal from the market, and, in particular, during its use. In order to facilitate this task, notably in conditions of use, high communication performance is required, this performance being expressed in terms of the possibility of interrogating the radiofrequency transponder at a long distance from the product, namely several meters, by means of a radiofrequency reader. Finally, it is desirable for the production cost of such a device to be as competitive as possible.
A radiofrequency transponder capable of meeting the requirements of tires is known from the prior art, notably from the document WO 2009/134243 A1. This transponder consists of an electronic chip, a printed circuit to which an electronic chip is electrically connected, and two metal helical springs connected mechanically and electrically to the printed circuit, forming a radiating dipole antenna. The communication with the radiofrequency reader uses radio waves, particularly the UHF (abbreviation of Ultra High Frequency) band. The characteristics of the helical springs, such as the wire diameter, the nature of the wire, the pitch of the helix and the length of the springs are therefore adjusted to the chosen communication frequency.
However, such a radiofrequency transponder has a number of drawbacks. Although part of the radiofrequency transponder is extensible, owing to the geometry of its antenna, there are still some areas of mechanical fragility with regard to high levels of stress in use. In particular, the mechanical connections between the helical springs and the printed circuit are rigid areas which form weak points for the endurance of the radiofrequency transponder.
Moreover, the process of manufacturing such a radiofrequency transponder is onerous. This is because the attachment of the helical springs to the printed circuit is a complicated operation, often performed manually, in which the ends of the three-dimensional helical springs must be fixed in the flat recess of the printed circuit, while the helical springs are also connected electrically to the tracks of the electronic circuit card. The latter operation cannot be performed using the conventional methods of the electronics industry.
Finally, the radiofrequency transponder must be fixed to the elastomer materials forming the tire. In particular, the joint between the rigid parts of the transponder and the elastomer products may require the use of special adhesion promoters.
The present invention relates to a radiofrequency transponder intended to improve the technical and economic performance of the radiofrequency transponders which are used in the tire industry as well as in other fields.